[unreadable] [unreadable] The six-year period between 18 and 24 years of age is critical in terms of the development of addictive behaviors. Marijuana use is particularly prevalent among young adults who smoke cigarettes, and there is reason to believe that the two behaviors should be approached concomitantly. This protocol describes a 4-year study that will investigate the effectiveness of two types of Brief Intervention (BI) for tobacco and marijuana use as linked to the Alcohol, Smoking and Substance Involvement Screening Test (ASSIST), a new screening test developed by the World Health Organization. Following initial exposure to smoking cessation therapy, 300 young adult cigarette smokers who are also marijuana users will be randomized to three conditions: 1) a wait list control group; 2) a group receiving one session of brief intervention for their marijuana use; and 3) a group receiving the same one session of MET along with a referral to an additional two sessions of brief therapy. Participants will be reinterviewed at 2, 4 and 6 months post randomization. The specific aims of the study are to answer the following questions: 1) Does exposure to smoking cessation therapy reduce marijuana smoking? 2) Does a marijuana-specific BI reduce marijuana use following smoking cessation therapy? 3) Does the more intensive three-session intervention reduce marijuana use more than one session? And 4) Are these interventions equally effective across groups defined by gender and ethnicity? The long-term objectives of the study are to develop screening and brief intervention procedures that will be feasible and effective in primary health care settings for the young adult population. [unreadable] [unreadable]